The present invention relates to a high-voltage current transformer of the head design having an insulative material column supporting a head housing and to a method of manufacturing such a high-voltage current transformer.
A high-voltage current transformer of this type is known from German No. A-16 13 798. This high-voltage current transformer provides a sealing plate on a column made of insulating material. A cylindrical head hood assemblable from two flanged parts is mounted laterally on the plate. The hood-shaped upper part of the head hood is provided with two side openings through which, in the usual fashion, the rod-shaped primary leads are fed. An electrical contact is made at an opening between the primary lead and the hood, while the primary lead is insulated where it is fed through the other opening. The rod-shaped primary lead passes through the annular core or cores of the secondary system in the horizontal direction. The annular cores of the secondary system are enclosed in a metallic grounded core capsule. The core capsule is then mounted along with the annular cores by a conical insulator on the sealing plate of the insulating column and supported therewith. The head hood is divided transversely for assembly reasons and is therefore designed in the form of two shells.
In addition, a high-voltage current transformer is known from German No. A-27 28 191 in which a sealing plate is provided on a column made of insulating material, on which plate a cylindrical head hood, in a lying position, is welded to the sealing plate and is connected to a lateral outlet opening, located beneath via a molded shaft. The primary lead is fed through the standing annular cores of the secondary system parallel to the horizontal lengthwise axis of the head hood and is brought in or out at the ends of the head hood each provided with an opening. The annular cores of the secondary system are enclosed in a metallic grounded core capsule. The core capsule is supported either on the ends of the head hood and/or on the lead tube for the secondary leads, which passes through the insulating column. For improved installation, the head hood is divided lengthwise and thus made in the form of two shells.
Both known designs of a high-voltage current transformer with a head hood therefore have not only three openings which must be tightly sealed during assembly for subsequent filling with insulating fluid or an insulating gas under pressure, but also have the transverse or lengthwise separating planes of the head housing which remain to be sealed.
The goal of the present invention is to design a high-voltage current transformer that permits simple manufacture of the head housing and a good seal with the smallest possible number of feedthroughs or separating planes to be sealed within the head housing or sealing plate. At the same time, the primary leads and secondary system must be capable of being mounted simply on the sealing plate of the insulating column.
This goal is achieved by mounting a secondary system having an annulus coil to a sealing plate and mounting a U-shaped primary lead having a horizontal base passing through the center opening of the secondary coil and having two legs mounted to the sealing plate. At least one of the legs of the primary lead passes through the sealing plate in an insulating-medium tight fashion to outside the space delineated by an insulating column, to which the sealing plate is mounted such that electrical contact can be made to the leg below the sealing plate. Electrical contact to the other leg may be made via the conductive sealing plate or it also may extend through the sealing plate in an insulating-medium tight fashion to outside the sealing plate where electrical contact may be made directly. The only other opening in the sealing plate is where the lead for the secondary system extends therethrough into the insulating column. A lead tube in the insulating column may be connected in a plug-in manner to the secondary lead of the secondary system. A hood is secured to the sealing plate and encompasses the secondary system and the primary leads therebetween. Other than a minimum of two and a maximum of three openings in the sealing plate, there are no other openings in the system and no openings in the hood.
The method of assembly is securing the secondary system to the sealing plate, inserting the U-shaped primary lead through the opening in the secondary system and securing it to the sealing plate, mounting the sealing plate to the insulative material column and securing the hood to the sealing plate either before securing the sealing plate to the insulative column or thereafter.
The secondary system is mounted to the sealing ring by insulative supports which engages at one end support surfaces on the sealing plate which are perpendicular to the longitudinal axis of the support. The supports are either secured internal to the sealing plate interior the hood, or using external screws which are covered by tight caps. The U-shaped primary lead may be composed of three elements being a base and two legs or of two elements being an angle and a single leg. The primary lead may be a single non-switchable lead or may be a dual-switchable lead formed from two concentric leads being switchable between separate, series or parallel connections. The legs may be flattened and displaced from the center axis of the fastener.
In the design for a high-voltage current transformer of the head design according to the invention, all the lateral openings in the head hood are eliminated and the head hood is completely relieved of the weight of the secondary system. Therefore, the head hood can be made of much thinner material, possibly even in one piece in a deep drawing process, and can thus be made much less expensively and lighter. The design of the high-voltage head current transformer according to the invention also permits all parts to be preassembled on the sealing plate and the unit thus preassembled can be mounted on the insulating column and fastened there. In addition, a controlled film feedthrough in the through opening of the secondary system, like that which is frequently conventional, can be eliminated. Therefore, a homogeneous insulating medium, especially an inert insulating gas such as sulfur hexafluoride or insulating oil can be used.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.